Positive Airway Pressure (PAP), including Continuous Positive Airway Pressure (CPAP), is a form of Noninvasive Positive Pressure Ventilation (NIPPV) for the treatment of Osbtructive Sleep Apnea (OSA). PAP treatment involves the delivery of a pressurized breathable gas, usually air, to a patient's airways using a conduit and a patient interface, for example, a mask. Gas pressures employed for CPAP treatment typically range from 4 cm H2O to 20 cm H2O, at flow rates of up to 180 l/min (measured at the patient interface), depending on patient requirements. The pressurized gas acts as a pneumatic splint for the patient's airway, preventing airway collapse, especially during the inspiratory phase of respiration.
CPAP machines including an airflow generator for supplying pressurized air to the patient are known, and over recent years there has been commercial incentive for more compact CPAP machines. However, in seeking to reduce the size of the CPAP machines there has been a trade-off between reduced size on the one hand and reduced performance on the other.
The advantages of incorporating humidification of the air supply to a patient are known, and CPAP machines are known which incorporate humidifying devices, either separately from the flow generator or integrated therewith. An example of an integrated flow generator/humidifier is the ResMed® S7 sold by the assignee of the present application. An example of a humidifier which is separately provided to be connectable to a flow generator is disclosed in co-pending, commonly assigned U.S. Patent Application Publication 2008/0072900 A1.
It is known to provide a heating unit, such as a heating plate, to a humidifier to increase the amount of water vapor in the flow of breathable gas. Reducing the size of CPAP machines, including humidifiers, has led to a decrease in the size of water containers making it more difficult to provide humidification of the air supply during the entirety of the patient's sleep cycle. The reduction in the size of humidifier tubs results in a decrease in the surface area of the water exposed to the flow of air provided by the flow generator. This creates problems in maintaining a sufficient moisture pickup. The integration of humidifiers with flow generators also makes it more difficult to clean the water container of the humidifier due to complex shapes of the tub and cover.
Humidifiers which are attachable to the flow generator also suffer from certain drawbacks. In some instances, the humidifier increases the size of the footprint of the device, meaning a table or stand may no longer be of suitable size to hold the device once the humidifier is attached. Some humidifiers also have seals that are submerged and that may tend to deteriorate over time with prolonged contact to water, increasing the propensity for leaks.
Some attachable humidifiers include a metal base to transfer heat from the heating plate to the water in the humidifier. The metal in these plates may corrode over time, reducing the effectiveness, even destroying, the humidifier. Additionally, extra electrical contacts need to be attached to the humidifier to provide power to the heating plate, and, since the heating plate is often positioned under the water supply, there is a design requirement to prevent spilled water from reaching electrical components.
The heat in the PAP device itself may often build up and reduce bearing life within the device. PAP devices also generate noise during operation, and this noise must be controlled so that it does not interfere with patient sleep.